The present invention relates to a voltage-controlled wavelength-selective photodetector and a method for it""s use.
Voltage-controlled wavelength-selective photodetectors can be used in optoelectronic converters for signal processing and for logical switching networks.
The article by Friedmann et al. in Compound Semiconductor, p. 27, November/December 1996, and the article by Fang et al. in IEEE Electron Device Letters Vol. 12, No. 4, Apr. 1, 1991, pp. 172-174 describe the use of photodetectors for detection of light having different wavelengths. European Patent Application No. 682 375 A1 also describes a photodetector that makes it possible to detect light having different wavelengths in the visible range using two detectors that are arranged one on top of the other and that are sensitive to different wavelengths. In addition, in German Patent Application No. (AZ 197 14 054 A1), filed prior to the date of the present application, but published after that date, describes a photodetector which is made of at least two photodiodes of silicon/silicon-germanium (Si/SiGe) semiconductor material arranged one on top of the other. These detectors are used, for example, in solar cells with the purpose of generating as high a photoelectric current as possible by adding the charges produced in the individual detectors. The use of different semiconductor materials contributes to achieving a high degree of spectral sensitivity in addition to a high degree of efficiency. The individual photoelectric currents produced in the detectors always overlap additively. Thus, while the use of various photodetectors to detect light signals is customary, the method of processing signals by subtraction of the photoelectric currents is not.
In order to separate a useful signal S from noise N and to improve the signal/noise ratio (S/N), expensive and complex signal decoding arrangements involving a plurality of detectors, beam splitters, filters, and additional electronics, are used.
An object of the present invention is therefore to provide a cost-effective, monolithically highly integratable photodetector that opens up possibilities of signal conversion in a broad spectrum through wavelength selectivity and can be used, in particular, to improve the signal/noise ratio of an optical signal.